JP6549477B2 - Wide-angle lens and imaging device - Google Patents

Description

  The present invention relates to a wide-angle lens and an imaging device, and more particularly to a wide-angle lens having a large aperture and an imaging device provided with the wide-angle lens.

  A wide-angle lens called a retrofocus type (reverse telephoto type) preceded by a negative lens group is widely known. For example, Patent Document 1 discloses a retrofocus wide-angle lens with an imaging angle of view of about 100 ° and an F number of 3.5. Such a retrofocus wide-angle lens has a large back focus as compared to the focal length of the entire lens system. Therefore, it can be suitably used as a lens interchangeable type imaging device such as a single-lens reflex camera.

  Generally, in a retrofocus wide-angle lens, a negative lens unit is disposed in front (object side), and a positive lens unit is disposed behind (image side). As described above, in the retrofocus wide-angle lens, since the refractive power arrangement in the entire system is asymmetrical, various aberrations such as spherical aberration, coma, distortion and astigmatism are easily generated. If a larger negative refracting power is placed in front to ensure a large back focus, the amount of aberrations generated will be larger. Therefore, it is very difficult to correct these aberrations in a well-balanced manner in a retrofocus wide-angle lens.

  Furthermore, in recent years, there has been a large demand from the market for increasing the diameter and reducing the size of wide-angle lenses. Therefore, in order to obtain a lens having a smaller f-number in a retrofocus wide-angle lens, the amount of generation of axial chromatic aberration and lateral chromatic aberration increases. Therefore, in addition to the various aberrations described above, it is also necessary to correct axial chromatic aberration and lateral chromatic aberration in a well-balanced manner.

  On the other hand, in the retrofocus wide-angle lens, while trying to reduce the diameter of the front lens while maintaining the imaging angle of view of about 100 ° and the f-number of 2.0 or less, the overall lens system was miniaturized. In this case, the amount of distortion aberration, astigmatism and the like increases. Therefore, it has been difficult to achieve high optical performance while maintaining the required back focus, angle of view, and f-number in a retrofocus wide-angle lens.

Patent No. 4946445

  An object of the present invention is to provide a compact wide-angle lens capable of achieving high optical performance while maintaining the required back focus, angle of view, and f-number, and an imaging apparatus including the wide-angle lens.

  In order to solve the above problems, the wide-angle lens according to the present invention comprises, in order from the object side, at least a first lens group having negative refractive power and a second lens group having positive refractive power. Focusing is performed by moving a lens group, and the first lens group includes at least three negative lenses and one positive lens, and the most object of the negative lenses included in the first lens group When the negative lens disposed on the side is a negative lens L1n, the negative lens L1n is characterized by satisfying the following conditions.

PgF-(0.6438-0.001682 x vd1n)> 0.006 (1)
d d 1 n <40 (2)
However,
PgF represents a partial dispersion ratio of g-line and F-line of the negative lens L1n,
ν d1 n represents an Abbe number for the d-line of the negative lens L 1 n.

  In addition, the imaging device of the present invention includes the wide-angle lens according to the present invention, and an imaging device for converting an optical image formed by the wide-angle lens into an electrical signal on the image plane side of the wide-angle lens. It is characterized by

  According to the present invention, it is possible to provide a compact wide-angle lens capable of achieving high optical performance while maintaining a predetermined back focus, angle of view, and f-number, and an imaging device provided with the wide-angle lens.

It is sectional drawing which shows the lens structural example at the time of infinity focusing of the wide angle lens of Example 1 of this invention. FIG. 6 is a longitudinal aberration diagram of the wide-angle lens of Example 1 at infinity focusing. However, spherical aberration, astigmatism and distortion are shown sequentially from the left toward the drawing. The same applies to the longitudinal aberration diagrams. 5 is a lateral aberration diagram showing coma aberration at infinity focusing of the wide-angle lens of Example 1. FIG. 5 is a longitudinal aberration diagram at the time of imaging magnification 1:40 of the wide-angle lens of Example 1. FIG. 5 is a lateral aberration diagram showing a coma aberration at the time of imaging magnification of 1:40 of the wide-angle lens of Example 1. FIG. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the wide angle lens of Example 2 of this invention. FIG. 6 is a longitudinal aberration diagram of the wide-angle lens of Example 2 when focused on infinity. FIG. 6 is a lateral aberration diagram representing coma aberration at infinity focusing of the wide-angle lens of Example 2. 5 is a longitudinal aberration diagram at the time of imaging magnification 1:40 of the wide-angle lens of Example 2. FIG. FIG. 7 is a lateral aberration diagram illustrating coma aberration at the time of imaging magnification of 1:40 of the wide-angle lens of Example 2. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the wide angle lens of Example 3 of this invention. FIG. 7 is a longitudinal aberration diagram of the wide-angle lens of Example 3 when focused on infinity. FIG. 6 is a lateral aberration diagram representing coma aberration when focusing at infinity of a wide-angle lens according to Implementation 3; FIG. 16 is a longitudinal aberration diagram at the time of imaging magnification 1:40 of the wide-angle lens of Example 3; FIG. 16 is a lateral aberration diagram illustrating a coma aberration at the time of imaging magnification of 1:40 of the wide-angle lens of Example 3.

  Hereinafter, embodiments of a wide-angle lens and an imaging device according to the present invention will be described.

1. Wide-angle lens 1-1. Configuration of Wide-Angle Lens The wide-angle lens according to the present invention comprises at least a first lens group having negative refractive power and a second lens group having positive refractive power in order from the object side, and at least the second lens group Focusing is performed by moving, and the first lens group includes at least three negative lenses and one positive lens, and one of the negative lenses included in the first lens group is When the negative lens L1n is used, the negative lens Ln1 is characterized by satisfying a predetermined condition described later. First, after describing the configuration of the wide-angle lens according to the present invention, matters concerning the conditional expression will be described.

  In the present invention, the first lens group having negative refractive power is disposed on the object side, and the second lens group having positive refractive power is disposed on the image side, to provide a so-called retrofocus lens configuration. . Therefore, it is easy to secure a sufficient back focus even when widening the wide-angle lens, and to secure a predetermined back focus required for interchangeable lenses of imaging devices such as single-lens reflex cameras. Can.

  Also, in general, in a wide-angle lens, an off-axis light beam incident at a large incident angle is converged by the first lens group. Therefore, in the wide-angle lens, the incident angle of the off-axis light beam with respect to the lens surface of the lens disposed on the object side in the first lens group is large, aberration is apt to occur, and the aberration amount tends to be large. Therefore, in the present invention, by making the first lens group include at least three negative lenses and one positive lens, generation of aberration can be suppressed and high optical performance can be realized. As described above, since the off-axis light flux can be corrected well, high optical performance can be realized over the entire screen.

  Furthermore, in the present invention, by adopting the above lens group configuration and performing focusing by moving at least the second lens group, it is possible to reduce aberration fluctuation due to focusing from infinity to near distance. Therefore, good optical performance can be realized over the entire focusing range regardless of the object distance. Hereinafter, preferable configuration examples of each lens group will be described.

(1) First Lens Group The first lens group has negative refractive power, and the specific configuration is not particularly limited as long as it has the above-described configuration. However, it is more preferable to adopt the following configuration.

  In the wide-angle lens according to the present invention, the first lens group includes, in order from the object side, a first A lens group having negative refractive power and a first B lens group having positive refractive power. Preferably, the first lens group B includes two or more negative lens components, and the first lens group B includes a negative lens component having a concave surface facing the object side. By adopting the configuration, it is possible to emphasize the retrofocus lens configuration. Therefore, even when the wide-angle lens is made wide-angle, it is easier to secure the predetermined back focus required for the wide-angle lens.

  However, in the present invention, the lens component includes a single lens, and a compound lens in which an aspheric resin is formed on one side or both sides of the lens. The lens component also includes a cemented lens in which two or more lenses are cemented. However, in the case of a cemented lens, the entire cemented lens is referred to as a lens component, and the negative lens component has negative refractive power when viewed in the cemented lens as a whole. At this time, when the cemented lens is referred to as a lens component, the object side surface means the surface disposed closest to the object side in the cemented lens, and the image side surface is disposed most on the image side in the cemented lens. Shall mean the face.

i) First A lens group In the first A lens group, it is preferable to dispose a meniscus negative lens having a convex surface facing the object side on the most object side. By arranging such a meniscus-shaped negative lens on the most object side of the first lens group A, occurrence of the above-mentioned various aberrations is caused even if an off-axis ray is incident on this meniscus-shaped negative lens at a large incident angle. It can be suppressed and it becomes easy to realize higher optical performance. Note that regardless of the specific configuration of the first lens group, that is, even when the first lens group is not composed of the first A lens group and the first B lens group, it is disposed on the most object side of the first lens group. The same effect as described above can be obtained by using a negative meniscus lens with a convex surface facing the object side.

  Further, in the first lens group A, it is preferable that the lens surface disposed closest to the image side be concave toward the image side. By placing the concave lens surface on the image side closest to the image side of the 1st lens group A, the aberration burden of the negative lens arranged on the object side of the 1st lens group 1 can be reduced, so It is easy to achieve wide angle and large aperture.

  Furthermore, the first lens group A is more preferably composed of three negative lens components. By adopting the configuration, it is possible to further emphasize the retrofocus-type lens configuration, and it is easy to achieve a wider angle and a larger aperture.

ii) First B lens group The retrofocus type lens configuration is further emphasized by configuring the first B lens group to include a negative lens component having a concave surface facing the object side, that is, a negative lens component having a concave object side surface. Even when the wide-angle lens is designed to have a wide angle, it is easier to secure a sufficient back focus.

  In order to obtain the effect, it is preferable that the negative lens component be disposed on the most object side of the first B lens group. When the image side surface of the negative lens component has a concave shape facing the image side, the curvature of the object side surface of the negative lens component is preferably larger than the curvature of the image side surface. Furthermore, it is preferable that the curvature of the object side surface of the negative lens component is the largest among the lenses having a concave shape on the object side surface included in the first lens group. As described above, the first lens group is composed of the first A lens group and the first B lens group, and a negative lens component in which the object side surface is a concave having a strong curvature is disposed on the most object side in the first B lens group. Thus, the following effects can be obtained. Generally, as the concave shape of the lens becomes stronger, the negative refractive power becomes stronger, so both spherical aberration and astigmatism act on the over side. However, when the above configuration is adopted, in the first B lens group, the concave surface disposed closest to the object side has variations in spherical aberration and astigmatism with respect to the refractive power of the surface in the opposite directions. That is, when the concave shape of the concave surface becomes strong, astigmatism acts on the over side, while spherical aberration acts on the under side in the reverse direction. Therefore, spherical aberration and astigmatism can be favorably corrected by adopting the above-described configuration and disposing the negative lens component having a concave surface with such a strong curvature on the most object side in the first lens group. It becomes.

  Further, the first lens group A and the first B lens are configured by arranging the first lens group in the above configuration and arranging a negative lens component that is a concave surface having a strong curvature on the object side surface on the most object side in the first B lens group. It becomes easy to appropriately set the refractive power balance in the group. As a result, in addition to the correction of the spherical aberration and the astigmatism described above, the correction of distortion becomes easy, various aberrations can be corrected in a well-balanced manner, and it becomes easy to realize higher optical performance.

  Furthermore, in the first B lens group, it is preferable that the image side surface of the lens disposed closest to the image side, that is, the lens surface disposed closest to the image side has a convex shape on the image side. By disposing a convex lens surface on the image side closest to the image side of the 1B lens group, it is possible to satisfactorily correct distortion generated by the negative lens disposed on the 1A lens group, and higher It becomes easy to realize optical performance. In addition, regardless of the specific configuration of the first lens group, the same effect as described above can be obtained by making the lens surface disposed closest to the object side of the first lens group convex toward the image side. .

(2) Second lens group The specific lens configuration is not particularly limited as long as the second lens group has positive refractive power as a whole. For example, the second lens group preferably includes at least one negative lens. By disposing at least one negative lens in the second lens group having positive refractive power, it is possible to suppress aberration fluctuation at the time of focusing, and to perform good aberration correction over the entire focusing range. Become.

(3) Aperture Stop In the wide-angle lens according to the present invention, the arrangement of the aperture stop is not particularly limited. However, in order to achieve the object of the present invention, the aperture stop is preferably disposed in the second lens unit or on the image side of the second lens unit. The diameter of the axial luminous flux incident on the second lens group is converged by the second lens group or the second group front group closer to the object than the aperture stop. Therefore, if the aperture stop is disposed in the second lens group or on the image side of the second lens group, the size of the aperture stop can be reduced. As a result, it is possible to reduce the size and weight of the drive mechanism for driving the aperture stop. Therefore, it is easy to reduce the size and weight of the wide-angle lens.

1-2. Lens Group Configuration The wide-angle lens may be provided with the above-described first lens group and second lens group, and the following lens group may be provided on the image side of the second lens group. For example, a third lens group or the like having a positive or negative refractive power can be disposed on the image side of the second lens group. At this time, the specific lens configuration and the like of the subsequent lens unit is not particularly limited.

1-3. Operation at the time of focusing In the wide-angle lens according to the present invention, by moving the second lens unit along the optical axis, as long as focusing is performed, the other fixing / moving of the other lens units at the time of focusing is particularly limited. It is not a thing. However, from the viewpoint of reducing the weight of the focus group, it is preferable that the first lens group be fixed in the optical axis direction at the time of focusing. When a lens group is provided on the image side of the second lens group, focusing may be performed by moving the lens group having positive refractive power at the time of focusing. At this time, it may be moved by the same moving amount as the second lens unit, or may be moved by a different moving amount. However, as in the case of the first lens group, from the viewpoint of reducing the weight of the focus group, it is preferable that the subsequent lens group be fixed at the time of focusing.

  For example, it is preferable to dispose a third lens group having positive refractive power via an aperture stop on the image side of the second lens group, and to make only the second lens group a focus group. If this configuration is adopted, the second lens unit can be configured with a small number of lenses, and downsizing and weight reduction of the focusing unit can be achieved. Therefore, quick focus operation is possible.

1-4. Conditional Expressions Next, conditions that the wide-angle lens according to the present invention should satisfy, or conditions that should be satisfied will be described.

  In the wide-angle lens according to the present invention, when any one of the negative lenses L1n among the negative lenses included in the first lens group is used, the negative lens L1n is expressed by the following conditional expression (1) and conditional expression (2) Satisfy the conditions shown.

Conditional Expression (1): PgF− (0.6438−0.001682 × dd1n)> 0.006
Conditional Expression (2): d d 1 n <40

However,
PgF represents the partial dispersion ratio of the g-line to the F-line of the negative lens L1n,
ν d1 n represents the Abbe number for the d-line of the negative lens L 1 n.

  Here, it is assumed that the refractive index of the glass for g-line (435.8 nm), F-line (486.1 nm), d-line (587.6 nm) and C-line (656.3 nm) is Ng, NF, Nd, NC, respectively. The Abbe number (νd) and the partial dispersion ratio (PgF) can be expressed as follows.

d d = (Nd-1) / (NF-NC)
PgF = (Ng-NF) / (NF-NC)

  The partial dispersion ratio (PgF) is a portion of C7 (glass material) (partial dispersion ratio 0.5393, dd: 60.49) and F2 (glass material) (partial dispersion ratio 0.5829, dd: 36.30) When the straight line passing through the variance ratio and the coordinate of d d is used as a reference line, it means the deviation of the partial dispersion ratio from the reference line.

1-4-1. Conditional expression (1)
First, the conditional expression (1) will be described. Conditional expression (1) defines the so-called anomalous dispersion of any one negative lens L1n of the at least three negative lenses included in the first lens group. By satisfying the conditional expression (1), for example, the secondary spectrum of lateral chromatic aberration can be favorably corrected even when attempting to increase the aperture while maintaining the angle of view of about 100 °, A compact, wide-angle lens with high performance can be realized.

  On the other hand, when the numerical value of the conditional expression (1) becomes equal to or less than the lower limit value, it becomes difficult to satisfactorily correct the secondary spectrum of lateral chromatic aberration. Therefore, it becomes difficult to realize high optical performance while maintaining a predetermined back focus, angle of view and F number. In addition, in order to realize good optical performance, the number of lenses for aberration correction increases, and it becomes difficult to miniaturize the wide-angle lens.

  In the wide-angle lens, the negative lens L1 n preferably satisfies the condition represented by the following conditional expression (1) ′, and more preferably satisfies the condition represented by the conditional expression (1) ′ ′. By satisfying these conditions, the effects of the present invention can be exhibited more.

Conditional Expression (1) ′: PgF− (0.6438−0.001682 × νd1n)> 0.01
Conditional Expression (1) ′ ′: PgF− (0.6438−0.001682 × νd1n)> 0.013

  Further, among the negative lenses included in the first lens group, the negative lens L1 n is more preferably a negative lens disposed closest to the object side in the first lens group in order to obtain the above-mentioned effect.

1-4-2. Conditional expression (2)
Conditional expression (2) defines the Abbe number of the negative lens L1n for the d-line. By satisfying the conditional expression (2), for example, it is possible to correct the chromatic aberration of magnification well even when attempting to increase the aperture while maintaining the angle of view of about 100 °, and the small size with high optical performance. Can achieve a wide-angle lens.

  On the other hand, when the numerical value of the conditional expression (2) becomes equal to or more than the upper limit value, it becomes difficult to satisfactorily correct the magnification chromatic aberration. Therefore, as in the case of the conditional expression (1), it becomes difficult to realize high optical performance while maintaining a predetermined back focus, angle of view and F number. In addition, in order to realize good optical performance, the number of lenses for aberration correction increases, and it becomes difficult to miniaturize the wide-angle lens.

  In the wide-angle lens, the negative lens L1 n preferably satisfies the condition represented by the following conditional expression (2) ′, and more preferably satisfies the condition represented by the conditional expression (2) ′ ′. By satisfying these conditions, the effects of the present invention can be exhibited more.

Condition (2) ': d d1 n <35
Condition (2) ′ ′: d d1 n <30

1-4-3. Conditional expression (3)
In the wide-angle lens according to the present invention, in the first lens group, at least one negative lens is disposed on the image side of the negative lens L1n, and any one negative lens disposed on the image side of the negative lens L1n. It is preferable that the negative lens L2n satisfies the condition represented by the following conditional expression (3), where 負 is a negative lens L2n.

  Conditional Expression (3): d d 2 n> 65

However,
ν d 2 n represents the Abbe number for the d-line of the negative lens L 2 n.

  Conditional expression (3) defines the Abbe number of the negative lens L2n with respect to the d-line. By configuring the first lens group using the negative lens L2n that satisfies the conditional expression (3), it becomes easy to reduce the lateral chromatic aberration, particularly the width of the F line and the C line, and higher optical performance can be achieved. It becomes easy to realize. On the other hand, when the numerical value of the conditional expression (3) becomes equal to or less than the lower limit value, it is difficult to reduce the width of the chromatic aberration of magnification, particularly the F line and the C line. However, the negative lens L2n may be any negative lens other than the negative lens L1n disposed closest to the object among the negative lenses included in the first lens group.

1-4-4. Conditional expression (4)
It is preferable that the wide-angle lens according to the present invention satisfies the condition represented by the following conditional expression (4).

Conditional Expression (4): D × Y / f ² > 0.4

However,
D represents the entrance pupil diameter,
Y represents the maximum image height,
f represents the focal length of the whole wide-angle lens system.

  Conditional expression (4) defines the range of the entrance pupil diameter with respect to the focal length of the whole wide-angle lens system. When conditional expression (4) is satisfied, correction of axial chromatic aberration and lateral chromatic aberration can be effectively performed by the negative lens which satisfies conditional expression (1). However, in the conditional expression (4), the focal length of the whole wide-angle lens system means a value at the time of infinity focusing. The focal lengths of the first lens unit and the like shown in the conditional expression (5) and the like to be described later are all values at the time of infinity focusing.

  On the other hand, when the value of the conditional expression (4) becomes equal to or less than the lower limit value, the correction of the lateral chromatic aberration becomes excessive. Therefore, in order to realize high optical performance, it is necessary to increase the number of lenses constituting the wide-angle lens, and it becomes difficult to miniaturize the wide-angle lens.

  In the wide-angle lens, it is preferable to satisfy the condition represented by the following conditional expression (4) ′, and it is more preferable to satisfy the condition represented by the conditional expression (4) ′ ′. By satisfying these conditions, the effects of the present invention can be exhibited more.

Conditional Expression (4) ′: D × Y / f ² > 0.45
Conditional Expression (4) ′ ′: D × Y / f ² > 0.50

1-4-5. Conditional expression (5)
In the wide-angle lens according to the present invention, it is preferable that the first lens unit satisfies the following conditions.

  Conditional Expression (5): −f1 / f <7.0

However,
f1 represents the focal length of the first lens group,
f represents the focal length of the whole wide-angle lens system.

  Conditional expression (5) defines the ratio of the focal length of the first lens unit to the focal length of the entire wide-angle lens. By satisfying the conditional expression (5), the focal length of the first lens unit falls within an appropriate range, and various aberrations can be corrected well. Further, by satisfying the conditional expression (5), the focal length of the lens unit having a positive refractive power, which is disposed on the image side of the first lens unit, becomes within the appropriate range, and Aberration variation can be suppressed, and high optical performance can be obtained over the entire focus range.

  On the other hand, when the numerical value of the conditional expression (5) exceeds the upper limit value, the exit pupil position moves to the image side, and it becomes difficult to form a retrofocus lens configuration. Therefore, it becomes difficult to secure the required predetermined back focus. Also, in this case, the focal length of the lens unit having a positive refractive power, which is disposed closer to the image than the first lens unit, becomes long, and it becomes difficult to suppress the aberration fluctuation during focusing. In particular, the distortion is under-corrected and the correction becomes difficult.

  In the wide-angle lens, it is preferable to satisfy the condition represented by the following conditional expression (5) ′, and it is more preferable to satisfy the condition represented by the conditional expression (5) ′ ′. By satisfying these conditions, the effects of the present invention can be exhibited more.

Conditional Expression (5) ': -f1 / f <6.5
Conditional Expression (5) ′ ′: −f1 / f <6.0

1-4-6. Conditional Expression (6) and Conditional Expression (7)
In the wide-angle lens according to the present invention, the first lens unit is constructed of, in order from the object, a first lens unit A including two negative lens components and a first lens unit B including a negative lens component concave on the object side. At the same time, it is preferable that the first A lens group satisfies the condition represented by the following conditional expression (6), and the first B lens group satisfies the condition represented by the following conditional expression (7).

Conditional Expression (6): 3.0> f1a / f1> 0.15
Conditional Expression (7): 10.0> f 1 b / f 1> −1.0

However,
f1a represents the focal length of the first A lens group,
f b1 represents the focal length of the first B lens group,
f1 represents the focal length of the first lens group.

  The conditional expression (6) and the conditional expression (7) are conditions that are preferably satisfied when the first lens group is composed of the first A lens group and the first B lens group described above. The conditional expression (6) and the conditional expression (7) define the combined focal length of each lens group with respect to the focal length of the first lens group. When the first A lens group and the first B lens group satisfy conditional expression (6) and conditional expression (7), respectively, the refractive power arrangement in the first lens group as the front group becomes appropriate, and the retrofocus type The lens configuration can be further emphasized, and various aberrations can be corrected well.

  On the other hand, when the numerical values of conditional expression (6) and conditional expression (7) become the upper limit value or more, the refractive power of the lens unit disposed on the image side relative to the first lens unit becomes relatively small. These corrections become difficult because coma aberration gets worse. On the other hand, when the numerical values of the conditional expression (6) and the conditional expression (7) become equal to or less than the lower limit value, the refractive power of the lens unit disposed on the image side of the first lens unit becomes relatively large. Since off-axis aberrations such as distortion and astigmatism are aggravated, these corrections become difficult.

  In the wide-angle lens, it is preferable to satisfy the conditions expressed by the following conditional expression (6) ′ and the conditional expression (7) ′, and expressed by the conditional expression (6) ′ ′ and the conditional expression (7) ′ ′ It is more preferable to satisfy the following conditions. By satisfying these conditions, the effects of the present invention can be exhibited more.

Conditional Expression (6) ': 2.5> f1a / f1> 0.17
Conditional Expression (7) ′: 9.0> f 1 b / f 1> −0.8

Conditional Expression (6) '': 2.0> f1a / f1> 0.19
Conditional Expression (7) ′ ′: 8.0> f 1 b / f 1> −0.6

1-4-7. Conditional expression (8)
In the wide-angle lens according to the present invention, when the first lens group includes the first A lens group and the first B lens group, the negative lens component included in the first B lens group has the following conditional expression (8 It is preferable to satisfy the condition represented by).

  Conditional Expression (8): Cr / f> −1.5

However,
Cr represents the curvature of the object side surface of the negative lens component included in the first B lens group,
f represents the focal length of the whole wide-angle lens system.

  When the negative lens component included in the first lens subunit B satisfies the conditional expression (8), the following effects can be obtained. Generally, as the concave shape of the lens becomes stronger, the negative refractive power becomes stronger, so both spherical aberration and astigmatism act on the over side. However, when the above configuration is adopted, in the first B lens group, the concave surface disposed closest to the object side has variations in spherical aberration and astigmatism with respect to the refractive power of the surface in the opposite directions. That is, when the concave shape of the concave surface becomes strong, astigmatism acts on the over side, while spherical aberration acts on the under side in the reverse direction. Therefore, spherical aberration and astigmatism can be favorably corrected by adopting the above-described configuration and disposing the negative lens component having a concave surface with such a strong curvature on the most object side in the first lens group. It becomes.

  According to the wide-angle lens of the above configuration, high optical performance is realized while maintaining an angle of view of about 100 ° and an f-number of 2.0 or less, and while reducing the diameter of the front lens, the entire lens system Can be miniaturized.

2. Imaging Device Next, an imaging device according to the present invention will be described. An imaging apparatus according to the present invention includes the wide-angle lens according to the present invention, and an imaging device provided on the image plane side of the wide-angle lens for converting an optical image formed by the wide-angle lens into an electrical signal. It is characterized by Here, the imaging device or the like is not particularly limited, and a solid-state imaging device or the like such as a CCD sensor or a CMOS sensor can also be used. The imaging device according to the present invention is suitable for an imaging device using such a solid-state imaging device such as a digital camera or a video camera. In addition, the imaging device may be a lens-fixed imaging device in which a lens is fixed to a housing. The wide-angle lens according to the present invention can ensure the back focus required for lens-interchangeable imaging devices such as single-lens reflex cameras and mirrorless single-lens cameras. Therefore, as a interchangeable lens of these lens-interchangeable imaging devices It is suitable.

  Next, the present invention will be specifically described by showing Examples and Comparative Examples. However, the present invention is not limited to the following examples. The wide-angle lens in each of the following examples is an imaging wide-angle lens used in an imaging device (optical device) such as a digital camera, a video camera, or a silver-halide film camera. In each lens sectional view, the left side is the object side and the right side is the image plane side.

(1) Configuration of Wide-Angle Lens FIG. 1 is a lens sectional view showing a lens configuration at the time of infinity focusing of a wide-angle lens according to a first embodiment of the present invention. The wide-angle lens comprises, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. It is done. At the time of focusing from an infinite distance object to a close distance object, with the first lens group G1 and the third lens group G3 fixed in the optical axis direction, the second lens group G2 is on the object side along the optical axis Moving. The aperture stop S is disposed on the object side of the third lens group G3.

  The first lens group G1 is composed of, in order from the object side, a first A lens group G1A of negative refractive power and a first B lens group G1B of negative refractive power.

  The first lens group G1A includes, in order from the object side, a negative meniscus lens L1 having a convex surface on the object side, a negative meniscus lens L2 having a convex surface on the object side, and a negative meniscus lens L3 having a convex surface on the object side It consists of The negative meniscus lens L2 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The first B lens group G1B is composed of, in order from the object side, a doublet-concave negative lens L4 and a cemented lens in which a positive lens L5 having a convex surface facing the image side is cemented. The cemented lens is the negative lens component having a concave surface with a stronger curvature on the object side.

  The second lens group G2 is composed of a positive meniscus lens L6 having a concave surface facing the object side, and a cemented lens having a negative meniscus lens L7 having a convex surface facing the object side and a positive lens L8. The positive meniscus lens L6 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The third lens unit L3 includes, in order from the object side, a cemented lens in which an aperture stop S, a negative meniscus lens L9 having a convex surface facing the object side, a positive lens L10, and a negative meniscus lens L11 having a concave surface facing the object side are cemented The negative lens L12, the positive lens L13, and the negative meniscus lens L14 having a concave surface facing the object side. The negative meniscus lens L14 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  However, in the wide-angle lens according to the first embodiment, focusing may be performed by moving the third lens unit along with the second lens unit along the optical axis. Even in that case, the effects of the present invention can be obtained.

  In FIG. 1, “IP” is an image plane, and specifically, indicates an imaging surface of a solid-state imaging device such as a CCD sensor or a CMOS sensor, a film surface of a silver salt film, or the like. Further, a cover glass (reference numeral omitted) is provided on the object side of the IP. This point is the same also in each lens sectional view shown in Example 2 and Example 3.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the wide-angle lens is applied will be described. Table 1 shows lens data of the wide-angle lens. In Table 1, "NS" is the order (surface number) of the lens surface counted from the object side, "R" is the curvature radius of the lens surface, "D" is the distance on the optical axis of the lens surface, and "Nd" is d The refractive index for a line (wavelength λ = 587.6 nm), and “ABV” indicates the Abbe number for the d line. Further, “ASPH” displayed in the next column of the surface number indicates that the lens surface is aspheric, and “STOP” indicates an aperture stop.

Table 2 shows aspheric surface data and variable intervals when the lens surface is aspheric.
The aspheric surface data indicates an aspheric coefficient when the aspheric surface shape is defined by the following equation. However, in the table, "E-a" indicates "x 10 ^-a ". In the following equation, “x” is the displacement from the reference plane in the optical axis direction, “r” is the paraxial radius of curvature, “H” is the height from the optical axis in the direction perpendicular to the optical axis, “k” "Is a conic coefficient, and" An "is an n-th order aspheric coefficient.

  The variable interval indicates an interval between each lens surface in focusing at infinity, at an imaging magnification of 1:40 (40 ×), and at closest object distance imaging (MOD).

  Further, Table 7 shows numerical values of the conditional expressions (1) to (7) and numerical values necessary for obtaining them. In Table 7, "Fno" is the F number, "f1" is the focal length of the first lens group, "f1a" and "f1b" are the focal lengths of the first A lens group and the first B lens group, respectively, "Y" Represents the maximum image height, “D” represents the entrance pupil diameter, and “Cr” represents the curvature of the object side surface of the negative lens component included in the first B lens group. The unit of length in each table is all "mm" and the unit of angle of view is all "°". The matters relating to these tables are the same as in each of the tables shown in the second to fifth embodiments, and therefore the description thereof will be omitted below.

  FIG. 2 and FIG. 3 show longitudinal aberration diagrams and lateral aberration diagrams of the wide-angle lens, respectively, at infinity focusing. 4 and 5 show longitudinal aberration diagrams and lateral aberration diagrams when imaging is performed at an imaging magnification of 1:40 of the wide-angle lens.

  In each longitudinal aberration diagram, spherical aberration, astigmatism, and distortion are represented in order from the left toward the drawing. In the figure representing spherical aberration, the vertical axis represents the ratio to the open F value, the horizontal axis represents defocus, the solid line represents d line (wavelength λ = 587.6 nm), and the dotted line represents g line (wavelength λ = 435.8 nm) Spherical aberration at In the diagram showing astigmatism, the vertical axis represents image height, the horizontal axis is defocused, the solid line represents the sagittal image plane (ds) for the d-line, and the dotted line represents the meridional image plane (dm) for the d-line. In a diagram showing distortion, the vertical axis represents image height, and the horizontal axis represents%, which represents distortion.

  In each lateral aberration diagram, an image point of 100% of the maximum image height (1.0 ω), an image point of 90% (0.9 ω), an image point of 70% (0.7 ω), and an image of 50% The lateral aberration at the point (0.5ω) and the on-axis point (0.0ω) is shown. In each lateral aberration diagram, the horizontal axis represents the distance from the chief ray on the pupil plane, and the solid line indicates the d-line and the dotted line indicates the coma at the g-line.

  The matters relating to these figures are the same as in the longitudinal aberration diagrams and the lateral aberration diagrams shown in Example 2 and Example 3, and thus the description thereof will be omitted below.

The back focus “BF” at the time of infinity focusing of the wide-angle lens is as follows. However, the following values do not include a cover glass having a thickness of 2 mm, and the same applies to the back focus shown in the other embodiments.
BF = 38.31867

(1) Configuration of Wide-Angle Lens FIG. 6 is a lens cross-sectional view showing a lens configuration at the time of infinity focusing of a wide-angle lens according to a second embodiment of the present invention. The wide-angle lens comprises, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. It is done. At the time of focusing from an infinite distance object to a close distance object, with the first lens group G1 and the third lens group G3 fixed in the optical axis direction, the second lens group G2 is on the object side along the optical axis Moving. The aperture stop S is disposed on the object side of the third lens group G3.

  The first lens group G1 is composed of, in order from the object side, a first A lens group G1A of negative refractive power and a first B lens group G1B of negative refractive power.

  The first lens group G1A includes, in order from the object side, a negative meniscus lens L1 having a convex surface on the object side, a negative meniscus lens L2 having a convex surface on the object side, and a negative meniscus lens L3 having a convex surface on the object side It consists of The negative meniscus lens L2 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The first B lens group G1B is composed of, in order from the object side, a doublet-concave negative lens L4 and a cemented lens in which a positive lens L5 having a convex surface facing the image side is cemented. The cemented lens is the negative lens component having a concave surface with a stronger curvature on the object side.

  The second lens group G2 is composed of a positive meniscus lens L6 having a concave surface facing the object side, and a cemented lens having a negative meniscus lens L7 having a convex surface facing the object side and a positive lens L8. The positive meniscus lens L6 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The third lens unit L3 includes, in order from the object side, a cemented lens in which an aperture stop S, a negative meniscus lens L9 having a convex surface facing the object side, a positive lens L10, and a negative meniscus lens L11 having a concave surface facing the object side are cemented And a negative meniscus lens L13 having a concave surface facing the object side. The negative meniscus lens L13 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  However, in the wide-angle lens according to the second embodiment, focusing may be performed by moving the third lens unit along with the second lens unit along the optical axis. Even in that case, the effects of the present invention can be obtained.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the wide-angle lens is applied will be described. Table 3 shows lens data of the optical system, and Table 4 shows aspheric surface data and variable intervals on the optical axis. Table 7 shows numerical values of conditional expression (1) to conditional expression (7). Furthermore, FIGS. 7 to 10 are longitudinal aberration diagrams and lateral aberration diagrams, respectively, at the time of focusing at infinity of the wide-angle lens and at the time of imaging at an imaging magnification of 1:40.

Further, the back focus at the time of infinity focusing of the wide-angle lens is as follows.
BF = 38.31987

(1) Configuration of Optical System FIG. 11 is a lens sectional view showing a lens configuration at the time of infinity focusing of the wide-angle lens of Embodiment 3 according to the present invention. The wide-angle lens is composed of, in order from the object side, a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power. At the time of focusing from an infinite distance object to a near distance object, the second lens group G2 moves to the object side along the optical axis with the first lens group G1 fixed in the optical axis direction. The aperture stop S is disposed in the second lens group G2.

  The first lens group G1 is composed of, in order from the object side, a first A lens group G1A of negative refractive power and a first B lens group G1B of negative refractive power.

  The first lens group G1A includes, in order from the object side, a negative meniscus lens L1 having a convex surface on the object side, a negative meniscus lens L2 having a convex surface on the object side, and a negative meniscus lens L3 having a convex surface on the object side It consists of The negative meniscus lens L2 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The first B lens group G1B is composed of, in order from the object side, a double concave negative lens L4 and a cemented lens in which a positive lens L5 having a convex surface facing the image side is cemented, and a double convex positive lens L6 There is. The cemented lens composed of the negative lens L4 and the positive lens L15 is the above-mentioned negative lens component having a concave surface with a stronger curvature on the object side.

  The second lens group G2 includes a cemented lens obtained by cementing a negative meniscus lens L7 having a convex surface on the object side and a positive lens L8, an aperture stop S, a negative meniscus lens L9 having a convex surface on the object side, a positive lens L10 and It comprises a cemented lens in which a negative meniscus lens L11 having a concave surface facing the object side is cemented, a biconcave negative lens L12, a biconvex positive lens L13, and a negative lens L14. The negative lens L14 is a glass mold type aspheric lens in which both surfaces are aspheric, or an aspheric lens by grinding.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the wide-angle lens is applied will be described. Table 5 shows lens data of the optical system, Table 3 [3b] shows aspheric surface data, and Table 6 shows variable intervals on the optical axis. Table 7 shows numerical values of conditional expression (1) to conditional expression (7). Furthermore, FIG. 12 to FIG. 15 are a longitudinal aberration view and a lateral aberration view, respectively, at the time of focusing at infinity of the wide-angle lens and at the time of imaging at an imaging magnification of 1:40.

Further, the back focus at the time of infinity focusing of the wide-angle lens is as follows.
BF = 38.75137

  According to the present invention, it is possible to provide a compact wide-angle lens capable of achieving high optical performance while maintaining a predetermined back focus, angle of view, and f-number, and an imaging device provided with the wide-angle lens.

G1 ··· First lens group G1A ··· First lens group G1B ··· First lens group G2 ··· Second lens group S ··· Aperture stop IP ··· Image plane

Claims (11)

From the object side, at least a first lens group having negative refractive power and a second lens group having positive refractive power,
Focusing is performed by moving at least the second lens group,
The first lens group includes at least three negative lenses and one positive lens, and one of the negative lenses included in the first lens group is a negative lens Ln1 . The negative lens Ln1 satisfies the following conditions ,
The first lens group includes, in order from the object side, a first A lens group including two negative lens components, and a first B lens group including a negative lens component having a concave surface facing the object side.
In the wide-angle lens, the lens disposed closest to the image side has a concave surface,
A wide-angle lens characterized by satisfying the following conditions.
PgF-(0.6438-0.001682 x vd1n)> 0.006 (1)
d d 1 n <40 (2)
3.0> f1a / f1> 0.15 (6)
10.0> f1b / f1> -1.0 (7)
However,
PgF represents a partial dispersion ratio of g-line and F-line of the negative lens L1n,
ν d1 n represents an Abbe number for the d-line of the negative lens L 1 n ,
f1a represents the focal length of the first lens group A,
f b1 represents the focal length of the first B lens group,
f1 represents the focal length of the first lens group. In the first lens group, at least one negative lens is disposed on the image side of the negative lens L1n, and any one negative lens disposed on the image side of the negative lens L1n is the negative lens L2n. 2. The wide-angle lens according to claim 1, wherein the negative lens L2n satisfies the following condition.
d d 2 n> 65 (3)
However,
ν d2 n represents an Abbe number for the d-line of the negative lens L 2 n. The wide angle lens according to claim 1 or 2 satisfying the following conditions.
D × Y / f ² > 0.4 (4)
However,
D represents the entrance pupil diameter,
Y represents the maximum image height,
f represents the focal length of the whole wide-angle lens system. The wide-angle lens according to any one of claims 1 to 3, wherein the first lens group satisfies the following condition.
−f 1 /f<6.0 (5)
However,
f1 represents the focal length of the first lens group ,
f represents the focal length of the whole wide-angle lens system. Among the negative lens component having a concave surface directed toward the object side in the first lens group, claims 1 to 4 of curvature of the object side surface of the negative lens component is the largest included in the 1B-th lens group The wide-angle lens according to any one of the above. The wide-angle lens according to any one of claims 1 to 5 , wherein the negative lens component included in the first B lens group satisfies the following condition.
Cr / f> -1.5 ... (8)
However,
Cr represents the curvature of the object side surface of the negative lens component included in the first B lens group,
f represents the focal length of the whole wide-angle lens system. The wide-angle lens according to any one of claims 1 to 6, wherein the first B lens group is configured of one negative lens component. The wide-angle lens according to any one of claims 1 to 6, wherein the first B lens group includes, in order from the object side, a negative lens component and a positive lens component. The wide-angle lens according to any one of claims 1 to 8 , wherein the first lens group is fixed in the optical axis direction. The wide-angle lens according to any one of claims 1 to 9 , further comprising an aperture stop on the image side of the second lens group. A wide-angle lens according to any one of claims 1 to 10 , and an imaging device for converting an optical image formed by the wide-angle lens into an electrical signal on the image plane side of the system. An imaging device characterized by

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